Recently, Amazon announced a program called KDP Select, which seemed like a promising idea. They asked for a 90-day renewable exclusive on distribution, and in exchange people can borrow my enrolled titles through Amazon Prime. Each borrow earns a proportional slice of a nice-sized pot that changes monthly. Also, writers are allowed to offer each enrolled title for free for up to five days. That sounds like a good marketing tool.
Some of my friends have legitimate concerns about this. Amazon has become so dominant, and writers are leery of being part of a behemoth that wants to take over the book world. I had similar feelings about Walmart until after settling into a new town, Walmart consistently offered the best deals on food and sundries for average people. So dealing with them is in my interest, and it's the same now with Amazon. They may deserve whatever labels we want to tag them with, but dealing with them is in my interest.
Combine that with Twitter, a free and easy social networking site, and you have a marketing combination that works better than anything else I've tried so far. My first promotion resulted in over 20,000 free downloads of When Pigs Fly, followed by a significant amount of paid sales. Without getting into numbers, I can say the results are great.
If you're an author looking for a way to market your ebooks, do yourself a favor and try this. If you don't want to deal with Amazon, perhaps you can try Smashwords. I have no experience with them, but friends have only good things to say. Either way you'll need to do your own proselytizing, and for that Twitter seems like a darned good tool.